Skull Confirms Older Origin for 'Living Fossil' Fish

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A group of ancient fish, called coelacanths, have changed so
little over time they are known as "living fossils." Now, the
remains of a skull found in the Yunnan Province of China,
confirms these creatures have been around, largely unchanged, for
more than 400 million years.

Once thought to have died out at roughly the time the dinosaurs
disappeared, the first living coelacanth was discovered in a
fishing net in 1938 off the eastern coast of South Africa. Since
then, others have turned up elsewhere along the coasts of the
Indian Ocean. [ Image Gallery: Freaky
Fish ]

While it's clear their history goes way back, the fossils they
left behind have been scarce so far. A lower jawbone, more than
400 million years old and discovered in Australia, hinted at the
earliest known
emergence of coelacanths whose appearance matched the two
species alive today. This small fossil has been described as the
oldest coelacanth, but the authors of the recent research write
that it offers so little information that it cannot be reliably
placed within the fishes' family tree.

The newest fossil evidence, the remains of a skull, date back to
almost the same time and contain more definitive features that
indicate both it and the Australian fossil were "modern"
coelacanths, according to the study researchers writing in the
April 10 issue of the journal Nature Communications.

The discovery reinforces what was already suspected about
coelacanths: After a period of rapid diversification long ago,
these fish have remained pretty much the same over hundreds of
millions of years, according to Matt Friedman, a lecturer in
paleobiology at the University of Oxford, who was not involved in
the research.

"It makes their sort of anatomical conservation, this lack of
major change over geological time, much more impressive,"
Friedman said.

In fact, the discovery extends the record for coelacanths with
modern-looking bodies back by about 17 million years, according
to the researchers, led by Min Zhu of the Chinese Academy of
Sciences.

Coelacanths belong to an ancient group, the lobe-finned fishes,
which have fins attached to stalks, rather than directly to their
bodies. More than 400 million years ago, the coelacanths are
believed to have split from off from other lobe-finned fishes,
which later gave rise to modern lung fishes and to tetrapods —
four-footed animals, including us.

So, our closest relatives among fishes are lung fish and the
living species of coelacanths, which belong to the genus
Latimeria, Friedman said.

Modern coelacanths are set apart by their symmetrical tail, a
relatively long snout and a jointed skull, which allows them to
open their mouths widely. More primitive
lobe-finned fish also have this joint; however, their skulls
are proportioned differently, according to Friedman.

The skull joint and the presence and position of large sensory
pores — part of a system fish use to detect changes in water
pressure — helped the researchers place the skull within the
coelacanths' family tree.